This middleware doesn't assume that you wish to use it for user authentication.
Instead, it only implements the oAuth authorization flow by creating a single
endpoint, for example, at:

/auth/dropbox

Point the user to /auth/dropbox when you want them to authorize to
the app. You can add your own custom parameters to the url.

After the user authorizes your app, they will be redirected back to /auth/dropbox
There, oauth-flow will put the authorization parameters in req.oauth then
call your custom middleware. Custom parameters that were passed when you sent the
user to /auth/dropbox/ will also be passed when returning.

What you do afterwards with the authorization data is entirely up to you.
You may create a new user, authenticate a user, add their account or do
something entirely different. You can redirect them to the original URL, or
alternaively if you opened the authorization dialog in a new window, simply
send a script to close the window - oauth-flow doesn't limit you to any particular
use.